The present invention relates generally to gauges for measuring fluid pressure and more particularly to a new and unique case for a fluid pressure gauge.
A frequent problem which has been encountered by those using fluid pressure gauges has been that the crystal, or transparent face plate of the gauge, usually requires replacement before any other portion of the gauge. The problem is that historically these face plates have been affixed to the gauge case in one of four different ways: (1) by retaining the face plate with a threaded ring which screws onto the outside surface of the gauge case, (2) by utilizing a molded plastic face plate having protuberances on its inside surface to engage the outer surface of the gauge cases in a friction fit relationship, (3) by utilizing a transparent plastic face plate which is secured to the outer surface of the gauge case by means of a set screw, and (4) a transparent plastic face plate which engages protuberances on the inside surface of the gauge case in a friction fit relationship. The problem has been that the suppliers of these gauges have been forced to stock all four different types of face plates so that they would have them readily available for replacement in the field. Additionally, it has been historically true that two types of gauge housings have been required, one for low pressure gauges and one for high pressure gauges. The low pressure gauges required the use of a wide Bourdon tube which necessitated the use of a recessed portion on the back plate to permit adequate clearance for the Bourdon tube to operate. The high pressure gauges did not include this recessed portion but did include blowout protection of some sort to make sure that some portion of the rearward portion of the gauge would blow before any other portion.